Methods and apparatuses for coating the interior surface of a casing, pipe or tube, with an alloy, such as a corrosion-resistant alloy, are disclosed. More specifically, methods and apparatuses are disclosed for metallizing the interior surface of metallic tubular bodies, to provide, for example, metallic casings with interior surfaces, coated with a corrosion-resistant and/or abrasion-resistant alloy coating to extend the useful life of the casings in harsh operating environments.
In many fields of endeavors, metallic casing pipes are used to transport fluids. Often, due to the extended length of the casings or tubings, ordinary or low-cost steel is used to fabricate the casing in order to reduce capital costs. However, the interior surface of metal casings are often exposed to corrosive or abrasive environments. For example, oil well casings are often exposed to high salinity water or acid, both of which promote corrosion of ordinary steels. In the area of chemical refining, the fluids transported through the casings may be abrasive or corrosive, or both.
Thus, it is often desirable to coat the interior surface of a steel casing with an alloy that is corrosion-resistant, abrasive-resistant, or both. While the interior coating of metallic casing adds to the cost of the casing, the coating of the interior surface of a steel casing is substantially cheaper than fabricating the entire casing from a corrosion-resistant and/or abrasive-resistant alloy.
The use of plating techniques is undesirable because plating, such as chrome plating, requires the use of chemical baths, which are environmentally undesirable and it is also difficult to deposit a plated layer with sufficient thickness to achieve the desired corrosion-resistant and/or abrasion-resistant effects.
The use of powder coating techniques are useful for coating the exterior surfaces of structures, but no efficient powder coating techniques have been developed for coating the interior surfaces of structures, such as metal casings. Similarly, the chemical vapor deposition and physical vapor deposition techniques, such as evaporation, ion plating, and sputtering, have not been adequately developed for coating interior surfaces such as the inside of a metal casing.
Another approach that has been used to metallize the interior of metallic casings involve the placing of alloy powder into the interior of the pipe and then heating the pipe with induction heating coils. However, the currently known techniques, as exemplified in U.S. Pat. Nos. 5,919,307, 5,413,638 and 5,059,453 all present certain operational problems. Specifically, the ""307 patent requires the coating alloy to be contained within a fluid degradable transport material and requires a casing to be coated to be filled with this material. The dispersion of coating alloy and transport material must be specially prepared and the ends of the casing must be sealed to prevent leakage. The technique disclosed in the ""638 patent requires the complex apparatus with a plurality of rollers designed to accommodate the metal casing as it changes in diameter while being heated and requires the casing to be passed through the heating apparatus. The costs required to construct the apparatus disclosed in the ""638 patent are substantial. The technique disclosed in the ""453 patent requires the coating materials provided in elongated rods that are placed longitudinally within the casing. Thus the elongated rods of alloy material must also be specially prepared. The induction heating process of the ""453 patent also requires a complex apparatus as the casing must be transported through the induction heating mechanism.
Thus, there is a need for an improved and simplified apparatus and method for coating the interior of metallic tubular bodies which is easier and less costly to employ.
In satisfaction of the aforenoted needs, methods for coating an interior surface of a metallic tube with an alloy are disclosed. One disclosed method comprises placing a quantity of an alloy in the tube, enclosing the ends of the tube with caps, at least one of which is vented, heating the tube with resistance heating by applying current across the tube sufficient to heat the tube and melt the alloy, and spinning the tube about a longitudinal axis of the tube to distribute the molten alloy along the interior surface of the tube using centrifugal forces generated by the spinning of the tube.
Apparatuses for coating an interior of a metallic tube with an alloy are also disclosed. One disclosed apparatus comprises a vertically adjustable support for supporting the metallic tube in a horizontal position. The apparatus also comprises at least two spaced-apart rollers and up to several sets of rollers in alignment with the vertical support for receiving the tube when the support is lowered to place the tube on the rollers in a horizontal position. At least one of the rollers is linked to a drive mechanism for rotating the roller and imparting rotation to the tube. The apparatus also includes two electrodes for detachable connection to opposing ends of the tube which are used to heat the tube, with the alloy disposed therein, prior to the placement of the tube on the rollers. The apparatus also includes two caps, at least one of which is vented for releasing gases generated during the heating and subsequent spinning of the tube. The apparatus may also include a supply of inert gas connected to one of the caps. The apparatus may also include a cooling mechanism such as a coolant spray device or a quench tank.